When working with an instrument in an area which is not clearly visible, it is of importance to detect or determine the current location of the instrument in order to be able to further process the detected location or position data in a suitable way. A known method is to furnish an instrument with electromagnetic position sensors and further to provide a field generator such that a control unit which is connected with the field generator and the position sensor(s) may detect position data of the instrument and display them on a display apparatus. From the essay “Plausibility check for error compensation in electromagnetic navigation in endoscopic sinus surgery” by Dirk Mucha et al., published as Proc. Computer Assisted Radiology and Surgery CARS, P. 3 17-18, 2006, it is known to furnish an instrument with two position sensors. For treating or handling a problem of field distortion by metallic devices, it is known to carry out a plausibility check of measured position measurement data. However, no method for additionally treating errors in the context of movements in a suitable way is known.